Polymers entropy-driven phase formation

Recently, new interesting phenomena that control the mode of packing of polymers have been found, and it has been shown that the basic principles of polymer crystallography are, in some cases, violated. In particular, (1) an atactic polymer can crystallize this is, for instance, the case of polyacrylonitrile [107] (2) in a crystalline polymer the chains can be nonparallel for instance, the structure of the yform of iPP is characterized by the packing of nearly perpendicular chains [108, 109] (3) the principle of entropy-driven phase formation may be violated and the high local symmetry of the chains is lost in the limit-ordered crystkhne lattice of polymers (symmetry breaking). 

In a polyelectrolyte solution, the phase transition is driven by electrostatic solute-solvent interaction which results in a gain in the configurational entropy and the formation of amorphous randomly mixed polymer-rich phase remaining in equilibrium with dilute supernatant. Physical conditions for phase separation are deduced exphcitly when the complexation between oppositely charged polyelectrolytes leads to self-charge neutralizahon. 

The phase separation of the solution is driven by the entropy of forming a liquid-crystalline phase at a high polymer concentration. However, Maier and Saupe [30] concluded that the formation of a nematic phase arises from orientation-dependent interaction of induced dipoles. From these considerations, it appears that both entropy and enthalpy contribute to the stability of mesophases, although in a different ratio for large and small molecules. Asymmetric at-... 

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